Allergies

Introduction

An allergy is a reaction the body has to a particular food or substance.

Allergies are very common. They're thought to affect more than one in four people in the UK at some point in their lives.

They are particularly common in children. Some allergies go away as a child gets older, although many are lifelong. Adults can develop allergies to things they weren't previously allergic to.

Having an allergy can be a nuisance and affect your everyday activities, but most allergic reactions are mild and can be largely kept under control. Severe reactions can occasionally occur, but these are uncommon.

Common allergies

Substances that cause allergic reactions are called allergens. The more common allergens include:

grass and tree pollen – an allergy to these is known as hay fever (allergic rhinitis)

Allergies occur when the body's immune system reacts to a particular substance as though it's harmful.

It's not clear why this happens, but most people affected have a family history of allergies or have closely related conditions such as asthma or eczema.

The number of people with allergies is increasing every year. The reasons for this are not understood, but one of the main theories is it's the result of living in a cleaner, germ-free environment, which reduces the number of germs our immune system has to deal with.

It's thought this may cause it to overreact when it comes into contact with harmless substances.

Is it an allergy, sensitivity or intolerance?

allergy – a reaction produced by the body's immune system when exposed to a normally harmless substance

sensitivity – the exaggeration of the normal effects of a substance; for example, the caffeine in a cup of coffee may cause extreme symptoms, such as palpitations and trembling

intolerance – where a substance causes unpleasant symptoms, such as diarrhoea, but doesn't involve the immune system; people with an intolerance to certain foods can typically eat a small amount without having any problems

The symptoms vary depending on what you're allergic to and how you come into contact with it. For example, you may have a runny nose if exposed to pollen, develop a rash if you have a skin allergy, or feel sick if you eat something you're allergic to.

See your GP if you or your child might have had an allergic reaction to something. They can help determine whether the symptoms are caused by an allergy or another condition. Read more about diagnosing allergies.

Severe allergic reaction (anaphylaxis)

In rare cases, an allergy can lead to a severe allergic reaction, called anaphylaxis or anaphylactic shock, which can be life-threatening.

This affects the whole body and usually develops within minutes of exposure to something you're allergic to.

Diagnosis

If you think you have an allergy, tell your GP about the symptoms you're having, when they happen, how often they occur and if anything seems to trigger them.

Your GP can offer advice and treatment for mild allergies with a clear cause.

If your allergy is more severe or it's not obvious what you're allergic to, you may be referred for allergy testing at a specialist allergy clinic. The tests that may be carried out are described below.

Skin prick testing

Skin prick testing is one of the most common allergy tests.

It involves putting a drop of liquid onto your forearm that contains a substance you may be allergic to. The skin under the drop is then gently pricked with a needle. If you are allergic to the substance, an itchy, red bump will appear within 15 minutes.

Skin prick testing is painless and very safe. Make sure you don't take antihistamines before the test, as they can interfere with the results.

Blood tests

Blood tests may be used instead of, or alongside, skin prick tests to help diagnose common allergies.

A sample of your blood is removed and analysed for specific antibodies produced by your immune system in response to an allergen.

Patch tests

Patch tests are used to investigate a type of eczema known as contact dermatitis, which can be caused by your skin being exposed to an allergen.

A small amount of the suspected allergen is added to special metal discs, which are then taped to your skin for 48 hours and monitored for a reaction.

Elimination diet

If you have a suspected food allergy, you may be advised to avoid eating a particular food to see if your symptoms improve.

After a few weeks, you may then be asked to eat the food again to check if you have another reaction.

Don't attempt to do this yourself without discussing it with a qualified healthcare professional.

Challenge testing

In a few cases, a test called a food challenge may also be used to diagnose a food allergy.

During the test, you're given the food you think you're allergic to in gradually increasing amounts, to see how you react under close supervision.

This test is riskier than other forms of testing, as it could cause a severe reaction, but is the most accurate way to diagnose food allergies. And challenge testing is always carried out in a clinic where a severe reaction can be treated if it does develop.

Allergy testing kits

The use of commercial allergy-testing kits isn't recommended. These tests are often of a lower standard than those provided by the NHS or accredited private clinics and are generally considered to be unreliable.

Allergy tests should be interpreted by a qualified professional who has detailed knowledge of your symptoms and medical history.

Medications for mild allergies are available from pharmacies without a prescription, but always ask your pharmacist or GP for advice before starting any new medicine, as they're not suitable for everyone.

Antihistamines

Antihistamines are the main medicines for allergies. They can be used:

as and when you notice the symptoms of an allergic reaction

to prevent allergic reactions – for example, you may take them in the morning if you have hay fever and you know the pollen count is high that day

Antihistamines can be taken as tablets, capsules, creams, liquids, eye drops or nasal sprays, depending on which part of your body is affected by your allergy.

Decongestants

Decongestants can be used as a short-term treatment for a blocked nose caused by an allergic reaction.

They can be taken as tablets, capsules, nasal sprays or liquids. Don't use them for more than a week at a time, as using them for long periods can make your symptoms worse.

Lotions and creams

Red and itchy skin caused by an allergic reaction can sometimes be treated with over-the-counter creams and lotions, such as:

Sprays, drops and weak steroid creams are available without a prescription. Stronger creams, inhalers and tablets are available on prescription from your GP.

Immunotherapy (desensitisation)

Immunotherapy may be an option for a small number of people with certain severe and persistent allergies who are unable to control their symptoms using the measures above.

The treatment involves being given occasional small doses of the allergen – either as an injection, or as drops or tablets under the tongue – over the course of several years.

The injection can only be performed in a specialist clinic under the supervision of a doctor, as there is a small risk of a severe reaction. The drops or tablets can usually be taken at home.

The aim of treatment is to help your body get used to the allergen so it doesn't react to it so severely. This won't necessarily cure your allergy, but it will make it milder and mean you can take less medication.

Treating severe allergic reactions (anaphylaxis)

Some people with severe allergies may experience life-threatening reactions, known as anaphylaxis or anaphylactic shock.

If you're at risk of this, you'll be given special injectors containing a medicine called adrenaline to use in an emergency.

If you develop symptoms of anaphylaxis, such as difficulty breathing, you should inject yourself in the outer thigh before seeking emergency medical help.

It's not the pet fur that causes an allergic reaction. Instead, it's flakes of their dead skin, saliva and dried urine.

If you can't permanently remove a pet from the house, you could try:

keeping pets outside as much as possible, or limiting them to a particular area of the house, preferably an area without carpet

not allowing pets in bedrooms

washing pets at least once a week

regularly grooming pets outside

regularly washing all bedding and soft furnishings on which a pet has lain

using an air filter in rooms where you spend most of your time

increase ventilation with fans, air-conditioning or by opening windows

If you're visiting a friend or relative with a pet, ask them not to dust or vacuum on the day you're visiting, as this will stir up the allergens into the air. Taking an antihistamine medicine about an hour before entering a pet-inhabited house can also help reduce your symptoms.

By law, food manufacturers must clearly label any foods that contain something that's known to cause allergic reactions in some people. By carefully checking the label for the list of ingredients, you should be able to avoid an allergic reaction.

People with food allergies most often experience an allergic reaction while eating out at a restaurant. You can avoid this by:

not relying on the menu description alone (remember, many sauces or dressings could contain allergens)

communicating clearly with the waiting staff and asking for their advice

avoiding places where there's a chance that different types of food could come into contact with each other, such as buffets or bakeries

Pollen allergies – more commonly known as hay fever – are caused when trees and grasses release pollen into the air. Doctors often call hay fever allergic rhinitis.

Different plants pollinate at different times of the year, so the months that you get hay fever will depend on what sort of pollen(s) you are allergic to. Typically, people are affected during spring (trees) and summer (grasses).

To help keep your hay fever under control, you can:

check weather reports for the pollen count and stay indoors when it's high, if possible

avoid drying clothes and bedding outside when the pollen count is high

wear wraparound sunglasses to protect your eyes

keep doors and windows shut when possible

shower and change your clothes after being outside

avoid grassy areas, such as parks and fields – particularly in the early morning, evening or night, when the pollen count is highest